Carbonaceous nanoparticles, methods of making same and uses thereof

ABSTRACT

Methods and compositions of carbonaceous nanoparticle fabrication and their use for electrode materials in supercapacitors are provided. The method includes a first step of reacting a first carbon source with a second carbon source in the presence of a nitrogen source in a DC arc furnace to form a composite nanoparticle. The second carbon source includes a dopant. The composite nanoparticle includes a crystalline carbon phase having an amorphous phase comprising dopant or carbide. The method includes a second step of removing the amorphous second layer to form the carbonaceous nanoparticle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of priority under 35 U.S.C. 119 to U.S.provisional patent application Ser. No. 61/970,988, filed Mar. 27, 2014,and entitled “Carbonaceous Nanoparticles, Methods of Making Same andUses Thereof,” the content of which is herein incorporated by referencein its entirety.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with government support under DMR-0843962awarded by the National Science Foundation. The government has certainrights in the invention.

FIELD

The present disclosure relates to methods for making carbon-basednanoparticles and their uses in supercapacitors.

BACKGROUND

A supercapacitor, which is also known as an ultracapacitor and formerlyknown as an electric double-layer capacitor (EDLC)) is a high-capacityelectrochemical capacitor with capacitance values up to 10,000 farads at1.2 volt that bridge the gap between electrolytic capacitors andrechargeable batteries. They typically store 10 to 100 times more energyper unit volume or mass than electrolytic capacitors, can accept anddeliver charge much faster than batteries, and tolerate many more chargeand discharge cycles than rechargeable batteries. They are however 10times larger than conventional batteries for a given charge.

Supercapacitors are used in applications requiring many rapidcharge/discharge cycles rather than long term compact energy storage:within cars, buses, trains, cranes and elevators, where they are usedfor recovery energy from braking, short-term energy storage orburst-mode power delivery. Smaller units are used as memory backup forstatic random-access memory (SRAM).

The salient feature of a supercapacitor is its ability to deliver muchhigher power density than a conventional battery. Supercapacitors areusually large devices owing to specific design requirements.Supercapacitors are constructed with two metal foils (currentcollectors), each coated with an electrode material such as activatedcarbon, which serve as the power connection between the electrodematerial and the external terminals of the capacitor. Specifically tothe electrode material is its very large surface area. The activatedcarbon is electrochemically etched, so that the surface of the materialis about a factor 100,000 larger than the smooth surface.

Supercapacitor electrodes are generally thin coatings applied andelectrically connected to a conductive, metallic current collector.Electrodes must have good conductivity, high temperature stability,long-term chemical stability (inertness), high corrosion resistance andhigh surface areas per unit volume and mass. Other requirements includeenvironmental friendliness and low cost.

The amount of double-layer as well as pseudocapacitance stored per unitvoltage in a supercapacitor is predominantly a function of the electrodesurface area. Therefore supercapacitor electrodes are typically made ofporous, spongy material with an extraordinarily high specific surfacearea, such as activated carbon. Additionally, the ability of theelectrode material to perform faradaic charge transfers enhances thetotal capacitance.

Generally, the smaller the electrode's pores, the greater thecapacitance and energy density. However, smaller pores increase (ESR)and decrease power density. Applications with high peak currents requirelarger pores and low internal losses, while applications requiring highenergy density need small pores. Carbon electrodes for use insuperconductors have been made with various carbon sources, includingactivated carbon, activated carbon fibers, carbon aerogel,carbide-derived carbon, graphene sheets, carbon nanotubes, onion-shapedcarbon nanoparticles and template carbon.

BRIEF SUMMARY

In a first aspect, a method of making a carbonaceous nanoparticle isprovided. The method includes two steps. The first step includesreacting a first carbon source with a second carbon source in a nitrogensource in a DC arc furnace to form a composite nanoparticle. The secondcarbon source includes a dopant. The composite nanoparticle includes acrystalline carbon phase having an amorphous phase comprising dopant orcarbide. The second step includes removing the amorphous second layer toform the carbonaceous nanoparticle.

In a second aspect, a supercapacitor is provided. The supercapacitorincludes a first electrode having a first substrate and carbonaceousnanoparticles; a second electrode comprising a second substrate andcarbonaceous nanoparticles; a separator positioned between the firstelectrode and the second electrode; and an electrolyte. The carbonaceousnanoparticles are preferably made according to the method of the firstaspect.

In a third aspect, a method of making an electrode for a supercapacitoris provided. The method includes the several steps. The first stepincludes applying to a substrate a suspension of a liquid dispersantcomprising carbonaceous nanoparticles formed according to the method ofthe first aspect. The second step includes drying the suspension ofcarbonaceous nanoparticles on the substrate. The third step includescompacting the dried suspension of carbonaceous nanoparticles on thesubstrate with a uniaxial pressure less than or equal to 1000 MPa tocreate an electrode.

These and other features, objects and advantages of the presentinvention will become better understood from the description thatfollows. In the description, reference is made to the accompanyingdrawings, which form a part hereof and in which there is shown by way ofillustration, not limitation, embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects and advantages other than those set forth abovewill become more readily apparent when consideration is given to thedetailed description below. Such detailed description makes reference tothe following drawings.

FIG. 1A depicts the morphological characterization of as-synthesizedBN—HCDN, wherein high-resolution SEM image of nanoparticles collectedfrom the chamber wall.

FIG. 1B depicts TEM image of a cluster of these nanoparticles on a holeycarbon grid.

FIG. 1C depicts high-resolution TEM images of as-synthesized BN—HCDN.

FIG. 2A shows EELS analysis results for the as-synthesized BN—HCDN,wherein STEM image of as elected BN—HCDN to be mapped by EELS.

FIG. 2B shows EELS spectrum of particle from FIG. 2A showing the B, C,and N edges of EELS.

FIG. 2C shows elemental mapping image of B (188-208 eV).

FIG. 2D shows elemental mapping image of N (401-421 eV).

FIG. 2E shows the over lay image of FIGS. 2C and 2D.

FIG. 3A illustrates the morphological characterization of annealedBN—HCDN (BN-1H), wherein high-resolution annular dark field-STEM imagesare shown.

FIG. 3B illustrates bright field high-resolution STEM images of singleBN-1H particle.

FIG. 3C illustrates a comparison of electron diffraction patternsbetween as-synthesized BN—HCDN (left) and BN-1H (right). Bright spots inthe right half indicate graphitic (crystalline) characteristics ofBN-1H, compared with the hazy pattern of as-synthesized BN—HCDN in theleft half.

FIG. 4A illustrates a porosity analysis from the BET measurement,wherein gas adsorption/desorption analysis using N2 (77.4 K) of theBN—HCDN before and after the annealing process for high-resolution N2isotherms.

FIG. 4B depicts the pore-size distribution of FIG. 4A (calculated byusing a slit NLDFT model).

FIG. 5A depicts XPS spectrum analysis for the N, BN, and BN-1H samplesfor a survey spectrum.

FIG. 5B depicts a high-resolution spectrum of C 1 s.

FIG. 5C depicts a high-resolution spectrum of B 1 s.

FIG. 5D depicts a high-resolution spectrum of N 1 s.

FIG. 6A illustrates electrochemical characterization in three electrodeconfiguration in a comparison study among the samples of N,as-synthesized BN, and BN-1H, wherein CV curves measured in 6 M KOHelectrolyte from −1.0 to 0 V at 100 mV s⁻¹.

FIG. 6B illustrates galvanostatic charge/discharge profiles at thecurrent density of 3 A g⁻¹.

FIG. 6C depicts an in-depth study of BN-1H, wherein Galvanostaticcharge/discharge profiles at different current densities obtained in 6 Mof KOH.

FIG. 6D depicts CV curves obtained in different electrolyte systems of 6M KOH and 1 M of H₂SO₄ at scan rate of 1 V s⁻¹.

FIG. 6E depicts an in-depth study of BN-1H, wherein Galvanostaticcharge/discharge profiles at different current densities obtained in 1 Mof H₂SO₄.

FIG. 7A depicts electrochemical characterization of thin filmsupercapacitor, wherein CVs profiles of a thin film supercapacitor ofBN-1H in a 6 M KOH, at different scan rates, from low to high.

FIG. 7B depicts galvanostatic charge/discharge curves at differentcurrent densities.

FIG. 7C depicts complex plane plot of the impedance analysis, with amagnification for the high-frequency region in the inset.

FIG. 7D depicts the real and imaginary part of the capacitance (C′ andC″) as a function of frequency. Very low relaxation time constant τ₀(8.5 ms) is confirmed.

While the present invention is amenable to various modifications andalternative forms, exemplary embodiments thereof are shown by way ofexample in the drawings and are herein described in detail. It should beunderstood, however, that the description of exemplary embodiments isnot intended to limit the invention to the particular forms disclosed,but on the contrary, the intention is to cover all modifications,equivalents and alternatives falling within the spirit and scope of theinvention as defined by the embodiments above and the claims below.Reference should therefore be made to the embodiments and claims hereinfor interpreting the scope of the invention.

DETAILED DESCRIPTION

The compositions and methods now will be described more fullyhereinafter with reference to the accompanying drawings, in which some,but not all permutations and variations of embodiments of the inventionare shown. Indeed, the invention may be embodied in many different formsand should not be construed as limited to the embodiments set forthherein. These embodiments are provided in sufficient written detail todescribe and enable one skilled in the art to make and use theinvention, along with disclosure of the best mode for practicing theinvention, as defined by the claims and equivalents thereof.

Likewise, many modifications and other embodiments of the compositionsand methods described herein will come to mind to one of skill in theart to which the invention pertains having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is to be understood that the invention is not to belimited to the specific embodiments disclosed and that modifications andother embodiments are intended to be included within the scope of theappended claims. Although specific terms are employed herein, they areused in a generic and descriptive sense only and not for purposes oflimitation.

Glossary of Terms and Definitions

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of skill in the artto which the invention pertains. Although any methods and materialssimilar to or equivalent to those described herein can be used in thepractice or testing of the present invention, the preferred methods andmaterials are described herein.

Moreover, reference to an element by the indefinite article “a” or “an”does not exclude the possibility that more than one element is present,unless the context clearly requires that there be one and only oneelement. The indefinite article “a” or “an” thus usually means “at leastone.”

As used herein, “about” means within a statistically meaningful range ofa value or values such as a stated concentration, length, molecularweight, pH, sequence identity, time frame, temperature or volume. Such avalue or range can be within an order of magnitude, typically within20%, more typically within 10%, and even more typically within 5% of agiven value or range. The allowable variation encompassed by “about”will depend upon the particular system under study, and can be readilyappreciated by one of skill in the art.

Ranges recited herein include the defined boundary numerical values aswell as sub-ranges encompassing any non-recited numerical values withinthe recited range. For example, a range from about 0.01 mM to about 10.0mM includes both 0.01 mM and 10.0 mM. Non-recited numerical valueswithin this exemplary recited range also contemplated include, forexample, 0.05 mM, 0.10 mM, 0.20 mM, 0.51 mM, 1.0 mM, 1.75 mM, 2.5 mM 5.0mM, 6.0 mM, 7.5 mM, 8.0 mM, 9.0 mM, and 9.9 mM, among others. Exemplarysub-ranges within this exemplary range include from about 0.01 mM toabout 5.0 mM; from about 0.1 mM to about 2.5 mM; and from about 2.0 mMto about 6.0 mM, among others.

Supercapacitor Designs with Nitrogen and Boron Co-Doped Carbon HDCN

A cost-effective approach to fabricate high performance supercapacitorsusing specially designed and processed nitrogen and boron co-dopedcarbon HDCN is presented. The process requires assembly ofclosely-interconnected nanoparticles with large internal/externalsurfaces and plenty of sub-nanochannels for high speed charge transport.The supercapacitor is formed under 700 MPa of uniaxial pressure toreduce the internal resistance of the device and to improve the powerdensity. This integrated approach provided a power density of nearly4.58 kW cm⁻³. In addition, an energy density of 2.45 mWhcm⁻³ was alsoobtained. The described fabrication process can be easily scalable formanufacturing.

The disclosed hierarchical design and assembly of the HCDN is based onvertically integrating optimal materials-performance at each lengthscale, ranging from the atomic to micrometers in length. At the atomiclevel, an abundance of active sites for chemical activity and chargeaccumulation are needed. At this level, doping the carbon with nitrogenand boron will alter its electronic properties as well as seeding thestructural change for the growth of the HCDN during synthesis. At thesub-nano level, abundant channels for efficient mass/charge transport ofelectrolyte species are needed within the nano-structure. At thenano-structure level, it is necessary to assure that the HCDN has ashape for optimum packing of charges and good electrical contact amongthe HCDN particles for rapid charge transport. Finally, at the micronlevel, the HCDN must be assembled and mechanically compacted between thetwo electrodes to deliver the maximum power density. Thus the elasticproperties of the HCDN were part of the design consideration. The HCDNsynthesis and characterization at each length scale is presented. Adiscussion of the supercapacitor fabrication and product performance ispresented in the examples.

In view of the foregoing, including the examples presented herein,specific aspects of the invention are now presented.

In a first aspect, a method of making a carbonaceous nanoparticle isprovided. The method includes two steps. The first step includesreacting a first carbon source with a second carbon source in thepresence of a nitrogen source in a DC arc furnace to form a compositenanoparticle. The second carbon source includes a dopant. The compositenanoparticle includes a crystalline carbon phase having an amorphousphase comprising dopant or carbide. The second step includes removingthe amorphous second layer to form the carbonaceous nanoparticle.

In one respect of the first aspect, the first carbon source is selectedfrom graphite and carbon black. In another respect, the dopant includesboron. In another respect, the dopant includes boron carbide (B₄C). Inanother respect, the ratio of the weight percent of the first carbonsource to the second carbon source comprising is from about 2:1 to about20:1. In one respect, the ratio of the weight percent of the firstcarbon source to the second carbon source includes a ratio of about 9:1.In another respect, the nanoparticle includes a substantially sphericalshape having nanohorns and nanographene sheets.

In a second aspect, a supercapacitor is provided. The supercapacitorincludes a first electrode having a first substrate and carbonaceousnanoparticles; a second electrode comprising a second substrate andcarbonaceous nanoparticles; a separator positioned between the firstelectrode and the second electrode; and an electrolyte. The carbonaceousnanoparticles are preferably made according to the method of the firstaspect.

In one respect, the supercapacitor includes a first substrate having afirst metal. In another respect, the supercapcacitor includes a firstmetal having stainless steel. In another respect, the supercapcacitorincludes a second substrate having a second metal. In another respect,the supercapcacitor includes a second metal having stainless steel. Inanother respect, the supercapcacitor includes a separator havingplastic. In another respect, the supercapcacitor includes a plastichaving polypropylene. In another respect, the supercapcacitor includes aplastic having a composition resistant to attack by acids and bases. Inanother respect, the supercapcacitor includes an electrolyte comprisingpotassium hydroxide. In another respect, the supercapcacitor includes anenergy density greater than or equal to about 2 mMwh/cm³. In anotherrespect, the supercapcacitor includes a power density of greater than orequal to about 4 kW/cm³.

In a third aspect, a method of making an electrode for a supercapacitoris provided. The method includes the several steps. The first stepincludes applying to a substrate a suspension of a liquid dispersantcomprising carbonaceous nanoparticles formed according to the method ofthe first aspect. The second step includes drying the suspension ofcarbonaceous nanoparticles on the substrate. The third step includescompacting the dried suspension of carbonaceous nanoparticles on thesubstrate with a uniaxial pressure less than or equal to 1000 MPa tocreate an electrode.

In one respect of the third aspect, the liquid dispersant comprises analcohol. In some respect, the alcohol is selected from a groupconsisting of ethanol, methanol and isopropyl alcohol. In anotherrespect, the substrate comprises a metal. In some respects, the metalcomprises stainless steel. In other respects, the first step of applyingcomprises spraying. For example, in some respects, spraying compriseselectro-spraying.

In other respects, the third aspect includes additional steps, such asrepeating the steps to create an additional electrode. In this regard,the electrode of this aspect further includes the step of providing aseparator. In some respects, separator comprises plastic. In otherrespects, the plastic comprises polypropylene.

In yet other respects, the method includes additional steps ofsandwiching the separator between the electrodes to create a drysupercapacitor. In this regard, the method includes an additional stepof providing electrolyte. In this regard, the electrolyte comprisespotassium hydroxide. In this regard, the method further includes thestep of soaking the dry supercapacitor with the electrolyte to createthe supercapacitor.

EXAMPLES

The invention will be more fully understood upon consideration of thefollowing non-limiting examples, which are offered for purposes ofillustration, not limitation.

Example 1 Nanoparticle Design and Synthesis BN—HCDN Fabrication andStructural Analysis

The first goal is to synthesize a HCDN with near spherical shapeconsisting of doped crystalline frame-work having numerous internalnano-channels and sharp tips for the transport and accumulation ofcharges. To achieve such an architecture the following two-stepprocessing sequence was taken to synthesize the unique HCDN: First, acomposite nanoparticle was synthesized consisting of fine lamella layersof crystalline carbon sandwiched between amorphous layers of nitrideand/or carbide materials. Second, the amorphous layers of the compositenanoparticle were selectively etched away by heating the sample in airat 450° C. to produce the desired structure.

DC arcs have been extensively used in nano-carbon studies [see, forexample, V. P. Dravid et al., Science 1993, 259:1601; X. K. Wang et al.,Appl. Phys. Lett. 1995, 66:2430; N. Li et al., Carbon 2010, 48:255; B.Lee et al., Energy Environ. Sci. 2012, 5:6941; X. Lin et al., Appl.Phys. Lett. 1994, 64:181]. To perform the first step, a DC arc wasconfigured as a high temperature furnace where a hole in the cathodeserves as a crucible that can be filled with materials to beincorporated into the products [S. P. Doherty et al., Carbon 2006,44:1511]. An optimal mixture of 90% graphite powder and10% B₄C powderwas used to synthesize the HCDN particles. B₄C was used primarily as asource for boron doping; nitrogen gas was used as the nitrogen sourcefor co-doping. The arc was operated with high purity nitrogen at 300Torr and a temperature around 3,000° C. Under these conditions, acomposite HCDN was obtained as proposed in step one described above.Nitrides and carbides in the HCDN remain amorphous while carbon achievedits crystalline form. (Note: HCDN samples were also synthesized withpure hydrogen and nitrogen gas only. However, the electrical-chemicalproperties of these samples were inferior, most likely due to theirstructural properties. Thus, this study focused on the B-N co-dopedsamples.)

The morphology of the as synthesized B-N co-doped HCDN (BN) collectedfrom the chamber wall is shown in the SEM image (FIG. 1A). The sphericalparticles are quite uniform in size, and they range between 40-60 nm. Atransmission electron microscopy (TEM) image, FIG. 1B, provides a closerview of a cluster of these particles on a holey carbon grid. FIG. 1C isa higher magnification of a composite particle showing the crystallinecarbon as the matrix embedded with amorphous materials. To study thecomposition of the as synthesized HCDN, electron energy lossspectroscopy (EELS) was used to map the locations of B, N, and C in theindividual particles, and X-ray photoelectron spectroscopy (XPS) wasused to study the average amount of each element and their local bondingenvironment over an assembly of nanoparticles. FIG. 2A shows a scanningtransmission electron microscopy (STEM) image of a selected nanoparticlemapped by EELS. STEM images and EELS were acquired in a probe-correctedJEOL ARM200F equipped with a GIF Tridiem operated at 80 kV. The electronenergy loss spectrum of the whole nanoparticle clearly shows the B, C,and N edges (FIG. 2B). From this mapping (FIGS. 2C-E) it is clear thatboth B and N are uniformly present across the nanoparticle indicatingthat the crystalline and amorphous phases of the composite HCDN arehomogeneously distributed within the particle.

In the second step of the synthesis, the amorphous materials in thecomposite HCDN was selectively etch-removed by heating the sample at450° C. in air. FIG. 3A is an annular dark field image of a typicalnanoparticle (BN-1H) after 1 hour of treatment to remove the amorphousmaterial from the nanoparticles. It shows how the dense nano-compositeparticle has transformed into a nano-porous particle. By furtherfocusing on a single nanoparticle (FIG. 3B), it is quite revealing tosee the transformation of a compact composite nanoparticle into acrystalline carbon “skeleton” framework, which consists of denselypopulated inter-nested carbon nano-horns [M. Yudasaka et al., Carbonnanotub. 2008, 111:605] and twisted nano-graphite sheets. The inset toFIG. 3B shows the fine structure of a typical nano-horn. An electrondiffraction pattern (FIG. 3C) was obtained from as deposited BN—HCDN(left half circle) and after 1-hour heat treatment, BN-1H (right halfcircle). The existence of diffraction spots in the rings indicates thepresence of randomly oriented carbon crystallites in the BN-1H sample.From the TEM images, it is clear that nanochannels have been createdwithin the particle that will improve charge transport. Second, thepresence of horn-shaped nanostructures will help to induce chargingeffects around their tips and promote local chemical activities.Thirdly, the inter-connection among the annealed HCDN particles willfurther enhance the charge flow among the assemblies of thesenanoparticles.

BN—HCDN Nanoparticle Porosity

While it is clear from the micrographs that selective etching cantransform a dense composite HCDN particle into a highly nano-porouscrystalline carbon nanoparticle, it is also desirable to quantify thechange in porosity that takes place. To this end, aBrunauer-Emmett-Teller (BET) pore structure analysis was carried out.The isotherms are Type II IUPAC classification without adsorptionhysteresis (FIG. 4A). The observed adsorption isotherm appears to berepresentative of an adsorption isotherm on a flat surface. The etchingprocess results in a remarkably enhanced N₂ adsorption uptake at lowrelative pressure (P/P₀), which is indicative of a huge increase innanoporosity. Moreover, continuous N₂ uptake can be observed in therelative pressure range of 0.3˜0.6, which also implies the presence oflarge increase in porosity. The pore size distribution was calculatedusing the quenched solid density functional theory (QSDFT) method thatwas part of the Quarda Win software package (Quanta chrome Instruments,USA), assuming a slit pore geometry. From this analysis there is only aminor amount of pores with characteristics in the micropore range forthe as synthesized BN sample.

On the other hand, there are two obvious peaks in the micropore rangefor the etched sample: one very sharp peak just above 1 nm and anotherbroad peak (with one tenth the height) between 2-3 nm (FIG. 4B). Thisdramatic increase in pore volume around 1 nm can be attributed to thepresence of numerous nanochannels and/or sub-nanochannels formed by theintertwined nano-carbon layers and nano-horns left behind in the etchednanoparticle discussed above [S. Bandow et al., Chem. Phys. Lett. 2000,321:514; S. Utsumi et al., J. Phys. Chem. B 2005, 109:14319]. As aresult, the surface area and pore volume of the etched sample increaseover the unetched sample from 193.3 m² g⁻¹ to 554.3 m² g⁻¹, and from0.27 cm³ g⁻¹ to 0.51 cm³ g⁻¹, respectively. It should be pointed outhere that these values remain nearly the same after the HCDN film iscompacted with a pressure of 700 MPa.

BN—HCDN XPS Analysis

Extensive XPS studies were performed on the BN and BN-1H particles. Fromthe survey spectrum of the N and BN samples (FIG. 5A) indicates theincorporation of N and B into these materials. The nitrogen and boronconcentrations in the as grown co-doped sample, BN, are about 4 at % and3 at % respectively (Table 1).

TABLE 1 Summary of XPS peak analysis for N, BN, and BN-1H samples. C¹ B²N³ Sample C-B C-C C-N C-O Content B-C B-N B-CO₂ B-O Content N-6 N-5 N-QN — 60.9% 21.1% 18.0% — — — 4.0 at % 71.7% 21.8% 6.5% BN 6.7% 69.7%13.2% 10.4% 3.0 at % 18.7% 50.5% 30.8% — 4.1 at % 58.8% 36.6% 4.6% BN-1h3.6% 72.3% 10.5% 13.5% 0.8 at % 15.7% 48.7% 27.7% 7.9% 2.2 at % 41.1%51.1% 7.8% ¹C-B (283.4 eV), C-C (284.6 eV), C-N (286.2 eV), and C-O(288.3 eV) ²B-C (189.5 eV), B-N (190.6 eV), B-CO₂ (192 eV), and B-O (193eV) ³N-6 (Pyridinic-398.5 eV), N-5 (Pyrrolic-400.5 eV), and N-Q(Quaternary-401.2 eV)

The predominate asymmetric C 1 s peak, shown in FIG. 5B, indicates theexistence of C—N, C—B, and/or C—O bonds in addition to C—C bonds. The C1 s spectrum could be deconvoluted into four peaks at 283.5, 284.7,286.3, and 288.4 eV; these were assigned to C—B, sp2 C═C, C—N, and/orC—O bonds, and π-π sp² satellite transitions respectively [S. Maldonadoet al., Carbon 2006, 44:1429; W. J. Hsieh et al., Carbon 2005, 43:820;P. Hammer et al., J. Vac. Sci. Technol. A 2000, 18:2277; H. Valdés etal. Langmuir 2002, 18:2111; K. László et al., Carbon 2001, 39, 1217; Y.C. Lin et al., Appl. Phys. Lett. 2010, 96:133110; S .T. Jackson et al.,Appl. Surf. Sci. 1995, 90:195]. The B1 s core level can be divided intomaximum 4 peaks of B—O (193 eV), BCO₂ (192 eV), B—N (190.6 eV) and B—C(189.5 eV) (FIG. 5C) [W. J. Hsieh et al. Carbon 2005, 43:820; Y. Kang etal., Carbon 2013, 61:200; S. H. Sheng et al., J. Mater. Chem. 2012,22:390]. The relatively large amount of B—N bonding indicates that Nfrom the reaction gas reacts preferentially with B over C when B ispresent. The high resolution N1 s peak can be deconvoluted into 3components (FIG. 5D); N-6 (398.6 eV), N-5 (400.6 eV), and N-Q (401.6 eV)[W. J. Hsieh et al., Carbon 2005, 43:820; Y. C. Lin et al. Appl. Phys.Lett. 2010, 96:133110]. N-6 corresponds to pyridinic substitution in thecarbon lattice, N-5 to pyrrolic substitution in the carbon latticeand/or B—N bonding, and N—Q to graphitic substitution in the carbonlattice. Considering large amount of B—N bonding indicated from the B1 sspectra, it can be assumed that there are also large amount of N—Bbonding, along with the pyrrolic N substitution, in peak N-6 in the Bdoped samples. As depicted above, due to the nature of ternary mixturein BN sample, there are large amount of different bonding at lowerbinding energy comparing with N sample (including N-6 and N-5). Althoughthe amount of Band N were somewhat decreased by the 1h annealing,sufficient quantities of B (0.8 at %) and N (2.2 at %) remain to changethe surface chemistry of the BN-1h sample thereby increasing itselectrochemical activities. Moreover, it should be noted that most ofthe nitrogen species present are as pyridinic (N-6) and pyrrolic (N-5)substitution. This is because nitrogen can act as an edge terminationagent during the graphene growth in a role similar to hydrogen in ahydrogen arc growth [Y. C. Lin et al., Appl. Phys. Lett. 2010,96:133110]. These N-6 and N-5 species are favorable for accumulatingcharges during supercapacitor operation due to their appropriateelectron configuration and binding energy [F. M. Hassan et al., J.Mater. Chem. A 2013, 1:2904]. Nitrogen bonding around the nano-graphiticedges favors pyridinic substitution [Lin et al. (2010)]; densityfunction theory (DFT) calculation indicates this should produce a p-typematerial [D. Usachov et al., Nano Lett. 2011, 11:5401]. XPS alsoindicates pyrrolic N-substitution where the Fermi level is in the middleof the gap. After annealing in air, the amount of oxygen species (suchas hydroxyl, ester, ketone, and carboxylic groups) on the surface of theHCDN were slightly increased from ca. 7 at % to 10 at %. Addition ofthese groups further enhances the redox reaction for more chargeaccumulation, and also increases the hydrophilic surface property forbetter wettability of the materials, which eventually increase theoverall electrochemical performance of BN-1H HCDN [M. Inagakia et al.,J. Power Sources 2010, 195:7880]. The difference in surface wettabilityof these samples with contact angle measurements was shown, wherein theBN-1H sample has the best wettability.

BN—HCDN Sample Densification

The HCDN nanoparticles were compacted or densified into a film underuniaxial pressure for the fabrication of supercapacitors. Thedensification of the HCDN film is needed to optimize the deviceperformance to obtain both the highest energy density and power density.This requires the optimization of at least two important parameters:charge density (amount of charge per volume) stored in the capacitor,and the supercapacitor charging and discharging rate (which requires theminimization of internal resistance of the device). In addition, thedevice needs to possess long-term stability through cycling.Densification is thus a key step to achieving these properties. Toassure the nanoparticle film was not over-compressed (beyond its elasticlimit), in-situ nano-indentation measurements were performed on singleselected BN-1H HCDN particles in a HR-TEM. An AFM-TEM in situ holderfrom Nanofactory AB was used to perform the compression experiments [G.Casillas et al., Philos. Mag. 2012, 92:4437; G. Casillas et al.,Jose-Yacaman, Nanoscale. 2013, 5:6333]. Briefly, the nanoparticles aredrop-casted onto an Au wire, which is mounted in to the AFM-TEM holderand once inside the TEM, they are compressed by a Si tip. The deflectionof the cantilever is used to compute the load applied on the particlesand the area of contact is estimated from the TEM images. The resultsshowed that a single nanoparticle was able to withstand ˜1000 MPa ofstress at the contact point without any deformation (except for thesharp tips). Beyond this stress the nanoparticle started to compressplastically. According to these results, an uniaxial pressure of 700 MPawas used to ensure that the nanoparticles were not damaged in the filmformation process discussed below (See, for example the BET isothermresult for compressed BN-1H sample).

BN—HCDN Electrical Measurement

Hall measurements were performed on normally ˜300 μm thick BN-1Hco-doped HCDN films. The HCDN particles were compacted under a uniaxialpressure of 700 MPa to form the films. The Hall mobility was determinedto be ˜2 cm²V⁻¹·s⁻¹ with a p-type carrier density of 5×10¹⁹ cm⁻³ toyield a conductivity of ˜15 S cm⁻¹. This carrier density is about oneorder of magnitude higher than an N-doped sample grown in the nitrogenarc without boron doping, while the p-type mobility is the same. Thus,the BN co-doped sample is more conductive by roughly a factor of 10.This information is very important to the design of the supercapacitor.To achieve high rates of charging and discharging, the internalresistance of the device needs to be very low.

BN—HCDN Electrochemical Analysis

As a demonstration of the advantage of its unique structure, theelectrochemical activity of B—N co-doped HCDN material was compared withN-doped HCDN samples using a three-electrode cell. FIG. 6A shows typicalcyclic voltammograms (CV) for a three-electrode cell in 6 M KOH at ascan rate of 100 mVs⁻¹. The as-deposited BN—HCDN exhibits a much largerCV curve than the N sample corresponding to superior electrochemicalactivities for storing charges. Considering the similar values forsurface area (193.3 m²g⁻¹ for the BN sample and 215 m²g⁻¹ for the Nsample), the increase in electrochemical activity is attributed to thesynergetic effect of B—N co-doping in the carbon structure as discussedearlier. Sharp response at the voltage changing point represents thefast charge/discharge characteristics owing to the favorable surfacechemical properties of B—N co-doping effects. Heteroatom doping in thecarbon framework changes the electronic properties of the material withthe heteroatoms being more favorable for the attraction of ions in theelectrolyte compared to that of the carbon atoms, thus inducing pseudocapacitance [F. M. Hassan et al., J. Mater. Chem. A 2013, 1:2904].Additionally, the presence of heteroatoms in the carbon matrix canenhance the wettability (hydrophilicity) between electrolyte andelectrode materials [E. Iyyamperumal et al., ACS Nano 2012, 6:5259].Therefore, the heteroatom doping could not only introduce extra pseudocapacitance but also enhance the electric double-layer capacitance. TheB—N co-doped synergetic effect becomes more significant after 1-hourannealing process. Due to the highly increased conductivity of the BN-1Hsample relative to the BN sample, faster response can be obtainedresulting in a nearly rectangular shaped CV curve. Moreover,characteristics of the redox reaction became more obvious showing theappearance of “humps” in the CV curves (FIG. 6A). Capacitive behaviorscan also be observed, exhibiting linear behavior during thegalvanostatic charge/discharge experiments performed at 3 Ag⁻¹ (FIG.6B). The specific capacitance of BN-1H sample was calculated from thedischarging curves with values of as high as 277 Fg⁻¹ at a currentdensity of 0.2 Ag⁻¹.

For the further validation of the advantages of B—N co-doping, anelectrochemical activity test was also performed in acidic media (1 M ofH₂SO₄). FIG. 6C shows charging/discharging scans as a function ofcurrent for 6 M KOH solution, while FIG. 6E shows that for 1 M H₂SO₄solution. FIG. 6D compares the differences in the electrolyte solutionsin C—V plots. The specific capacitance of the BN-1H was calculated fromgalvanostatic charge/discharge curves according to the relationC_(spec)=I·tm⁻¹·V⁻¹, where t is the charge/discharge current, t is thedischarge time, m is the mass of electrode material and V is the voltagedifference. The highest capacitance values, calculated from thedischarge curves, were 277 Fg⁻¹, and 245 Fg⁻¹ in 6 M KOH and 1 M H₂SO₄,respectively. Considering the surface area (554.3 m²g⁻¹), this value canbe converted to a considerably high value of 49.9 μFcm⁻² which is muchhigher value than 10˜30 μFcm⁻² which are typically showed in carbonmaterials [L. L. Zhang and X. S. Zhao, Chem. Soc. Rev. 2009, 38:2520; J.Han et al., ACS Nano 2013, 7:19]. This means the BN-1H has highlyelectrochemical-active surface characteristics.

Example 2 Supercapacitor Fabrication Fabrication and Properties ofTwo-Electrode BN—HCDN Supercapacitors

The above results demonstrate BN-1H particles have superiorelectro-chemical properties and thus should be used for the fabricationof the two-electrode supercapacitors. The steps taken to prepare thedevices are as follows: BN-1H carbon nanoparticles processed from thearc furnace as describe above are electro-sprayed onto two identicalstainless steel substrates to form thin films of BN-1H. In order toretain high efficiency (low internal resistance), no organic bindingmaterial has been used in assembly the BN-1H nanoparticles. The thinfilms are further compacted under a pressure of 700 MPa to a thicknessof ca. 1 μm. The two densified electrodes are sandwiched togethermechanically with a polypropylene separator layer between them. Thisassembly is then soaked in the 6 M of KOH electrolyte. FIG. 7 shows thecharacteristics of a typical supercapacitor. Cyclic voltammograms (CVs)were recorded at scan rates from 1,000 mV s⁻¹ to 10,000 mV s⁻¹ to testthe power capability of the thin film supercapacitor (FIG. 7A). Almostperfect rectangular shaped CV curves, up to the very high scan rate,indicate low resistance, as well as its high power characteristics forthe device. The galvanostatic charge/discharge curves at three currentdensities are shown in FIG. 7B. The specific capacitance was calculatedfrom the discharge curves with values of 28.3, 28.1, and 28.1 F cm⁻³obtained at current densities of 600, 1200, and 3000 mA cm⁻³,respectively (FIG. 7B).

Electrochemical impedance spectroscopy (EIS) further confirms thesuperior power performance of the compacted BN-1H thin filmsupercapacitor. The vertical feature in the Nyquist plot of BN-1H showsthe nearly ideal capacitive behavior of the cell. The equivalent seriesresistance obtained from the intercept of the plot on the real axis isonly 0.34 Ω cm⁻². From the expanded high-frequency range data (FIG. 7C,inset), a transition between the RC semicircle and the migration ofelectrolyte was observed at a frequency ca. 3000 Hz. The diffusion ofelectrolyte ions stopped ca. 400 Hz, and thereafter the full capacitancewas reached. The thin film supercapacitor of BN-1H shows superiorfrequency response with a very small relaxation time constant τ₀ of 8.5ms (τ₀ being the minimum time needed to discharge all the energy fromthe device with an efficiency of greater than 50% [P. Banerjee, I.Perez, L. Henn-Lecordier, S. B. Lee, G. W. Rubloff, Nat. Nanotech. 2009,4:292]; FIG. 7D). This small time constant for BN-1H is very promisingcompared with previously reported values for planarmicro-supercapacitors: activated carbon (700 ms) [D. Pech et al., Nat.Nanotech. 2010, 5:651], onion-like carbon (26 ms) [Pech (2010)] anddirect laser writing graphene device (19 ms) [M. F. El-Kady and R. B.Kaner, Nat. Commun. 2013, 4:1475]. The measured electrical properties ofthe BN-1H two-electrode supercapacitor give a high power density (4.58kW cm⁻³) and energy density (2.45 mWh cm⁻³). Furthermore, the thin filmBN-1H supercapacitors show excellent cycling stability, retaining ca.90% of the initial performance after 10,000 charge/discharge cycles.

Synthesis of Boron and Nitrogen Doped Arc Carbon Materials

The arc system used in this study is described in detail elsewhere [L.S. Wang et al., Appl. Phys. A 2007, 87:1]. Briefly, the arc consists oftwo electrodes. The cathode is a solid ⅜-inch diameter randomly orientedgraphite (ROG) rod. The anode is a cup-like structure fabricated from a⅜-inch diameter ROG rod with a 3/16-inch diameter hole, 4 inch deep, inthe center of the end facing the cathode. The hole, or cup, in the anodecup is filled with tightly compacted graphite powder; as a boron (B)source 10 wt % B₄C was mixed with graphite powder.

After the chamber was evacuated, 300 Torr of Nitrogen (N) gas wasintroduced. Nitrogen was used as nitrogen source. A 100 Amp DC arc wasapplied to heat the graphite powder inside the hole. A potential of27-28 V was maintained between the electrodes by adjusting the spacingbetween them, typically 0.5 to 0.7 inch. A typical synthesis experimentlasts ca. 7 min. The arc soot deposited on the surface of chamber wascollected.

Some graphite impurities exist in the as-collected soot, so apurification process was performed to remove un-desired carbon species.First, the as-collected sample was dispersed in a solution of water andethanol (9:1) and then sonicated to make a highly dispersed suspension.The suspension was centrifuged to remove heavy graphitic balls from thearc soot. After the centrifugation, the supernatant was freeze-driedovernight to yield the purified arc soot. This sample is designated asthe as-synthesized BN—HCDN herein. For the control experiment, puregraphite powder without B₄C addition was introduced into the arcdischarge process to produce soot doped with only nitrogen, which isdesignated as the N sample.

For the synthesis of the BN-1H sample, as-synthesized carbon sootunderwent a heat treatment in air at 450° C. to etch-remove of theamorphous portion of the material.

Characterization of Synthesized Materials

Scanning electron microscopic (SEM) images were obtained using a HitachiSU8030 field emission SEM (FESEM). Transmission electron microscopy(TEM), selected area electron diffraction (SAED) studies were performedusing a JEOL 2100F FAST TEM working at 200 kV. Structuralcharacterization of the arc carbon was done by X-ray diffraction (XRD,D/MAX-A, Rigaku) featuring Jade Analysis software. The surface area andpore size distribution of the synthesized HCDN were measured by nitrogenadsorption/desorption isotherms, using a Micrometrics ASAP 2020 system.The sample was degassed at 398 K under vacuum overnight before analysis,to remove any adsorbed impurities. The surface area was measured usingthe Brunauer-Emmett-Teller (BET) model for relative pressures and thedistribution of pore dimensions was calculated using theBarrett-Joyner-Halenda (BJH) model. XPS spectra were recorded on aThermo Scientific ESCALAB 250Xi. All binding energies (BEs) are referredto the graphitic C 1s line at 284.7 eV.

Compressing Test for the BN-1Sample

The in situ TEM experiments were performed in a JEOL JEM-2010F. Imageswere recorded with an AMT CCD camera. The sample was diluted in ethanol,ultrasonicated and drop-casted on to a 0.25-mm Au wire that was mountedon an N force-probing holder (AFM-TEM holder) from NanofactoryInstruments AB. The sample is mounted on a piezotube which enablesthree-dimensional movement with sub-nanometer precision. For loadmeasurements, this holder relies on the deflection of a siliconcantilever with a sharp tip. These experiments were carried out with acantilever of a spring constant of 2.3 nNm⁻¹. Finally, the stress can beestimated by assuming a circular area of contact and measuring thediameter from the TEM micrographs.

Electrochemical Characterization of Synthesized Materials

Three-electrode test: Electrochemical measurements were performed usingan AUTOLAB PGASTAT 302N potentiostat with a standard three-electrodesetup in both 6 M of KOH and 1 M H₂SO₄. Working electrodes were preparedby drop-casting the samples on a glassy carbon electrode: A Pt plate andan Ag/AgCl electrode saturated with KCl were used as a counter electrodeand reference electrode, respectively. Cyclic voltammograms wererecorded within the range from 0 to -1 V in KOH and from 0 to 1 V inH₂SO₄ at various scan rates. Galvanostatic charge/discharge was carriedout within the same voltage range of CV measurement at various currentdensities. Electrochemical impedance spectroscopy (EIS) measurement wascarried out by applying voltage amplitude of 10 mV at OCV (open circuitvoltage) in the frequency range from 100 kHz to 50 mHz.

Calculations: The capacitance of each device was calculated from thegalvanostatic charge/discharge curves using the formula:

For a three electrode configuration:

$C_{electrode} = \frac{i \times \Delta \; t}{\Delta \; V}$

Where i (A) is the discharge current, Δt (s) is the discharge time, ΔV(V) is the voltage change (excluding the iR drop) within the dischargetime. Gravimetric specific capacitance was calculated by dividingcapacitance by the mass of electrode material.

For a two electrode thin film configuration:

$C_{device} = {\frac{i \times \Delta \; t}{\Delta \; V} \times 4}$

Where i (A) is the discharge current, Δt (s) is the discharge time, ΔV(V) is the voltage change (excluding the iR drop) within the dischargetime, the multiplier of 4 adjusts the capacitance of the cell and thecombined mass of two electrodes to the capacitance and mass of a singleelectrode. Specific capacitance was calculated based on the volume ofthe device according to the following formula:

Volumetric capacitance (C _(v))=C _(device) /V

where V refers to the volume (cm³) of the device.

The energy density (Whcm⁻³) and power density (Wcm⁻³) derived from thecharge/discharge curves are calculated by the following equations:

$E = {C_{v} \times \frac{\Delta \; V^{2}}{2 \times 3600}}$$P = {\frac{\Delta \; V^{2}}{4} \cdot R_{ESR} \cdot V}$

For the calculation of maximum power density, R_(ESR)(equivalent seriesresistance) of the device was obtained from the EIS (Electrochemicalimpedance spectroscopy) measurements.

Incorporation by Reference

All of the patents, patent applications, patent application publicationsand other publications recited herein are hereby incorporated byreference as if set forth in their entirety.

The present invention has been described in connection with what arepresently considered to be the most practical and preferred embodiments.However, the invention has been presented by way of illustration and isnot intended to be limited to the disclosed embodiments. Accordingly,one of skill in the art will realize that the invention is intended toencompass all modifications and alternative arrangements within thespirit and scope of the invention as set forth in the appended claims.

The claimed invention is:
 1. A method of making a carbonaceousnanoparticle, comprising: reacting a first carbon source with a secondcarbon source in the presence of a nitrogen source in a DC arc furnaceto form a composite nanoparticle, wherein the second carbon sourcecomprises a dopant, wherein the composite nanoparticle comprises acrystalline carbon phase having an amorphous phase comprising dopant orcarbide; and removing the amorphous second layer to form thecarbonaceous nanoparticle.
 2. The method of claim 1, wherein the firstcarbon source is selected from graphite and carbon black.
 3. The methodof claim 1, wherein the dopant comprises boron.
 4. The method of claim1, wherein the dopant comprises boron carbide (B₄C).
 5. The method ofclaim 1, wherein the ratio of the weight percent of the first carbonsource to the second carbon source comprises from about 2:1 to about20:1.
 6. The method of claim 5, wherein the ratio of the weight percentof the first carbon source to the second carbon source comprises about9:1.
 7. The method of claim 1, wherein the nanoparticle comprises asubstantially spherical shape having nanohorns and nanographene sheets.8. A supercapacitor, comprising: a first electrode comprising a firstsubstrate and carbonaceous nanoparticles; a second electrode comprisinga second substrate and carbonaceous nanoparticles; a separatorpositioned between the first electrode and the second electrode; and anelectrolyte, wherein the carbonaceous nanoparticles are made accordingto the method of claim
 1. 9. The supercapacitor of claim 8, wherein thefirst substrate comprises a first metal.
 10. The supercapcacitor ofclaim 9, wherein the first metal comprises stainless steel.
 11. Thesupercapacitor of claim 8, wherein the second substrate comprises asecond metal.
 12. The supercapacitor of claim 11, wherein the secondmetal comprises stainless steel.
 13. The supercapacitor of claim 8,wherein the separator comprises plastic.
 14. The supercapacitor of claim13, wherein the plastic comprises polypropylene.
 15. The supercapacitorof claim 13, wherein the plastic comprises a composition resistant toattack by acids and bases.
 16. The supercapacitor of claim 8, whereinthe electrolyte comprises potassium hydroxide.
 17. The supercapacitor ofclaim 8, wherein the supercapacitor has an energy density greater thanor equal to about 2 mMwh/cm³.
 18. The supercapacitor of claim 8 having apower density, wherein the power density comprises greater than or equalto about 4 kW/cm³.
 19. A method of making an electrode for asupercapacitor, comprising: applying to a substrate a suspension of aliquid dispersant comprising carbonaceous nanoparticles formed accordingto the method of claim 1; drying the suspension of carbonaceousnanoparticles on the substrate; and compacting the dried suspension ofcarbonaceous nanoparticles on the substrate with a uniaxial pressureless than or equal to 1000 MPa to create an electrode.
 20. The method ofclaim 19, wherein the liquid dispersant comprises an alcohol.